The present invention relates to fluorescent maleimides of the formula I 
wherein
R1 and R2 independently from each other stand for 
wherein Q1 stands for hydrogen, halogen, phenyl, xe2x80x94Exe2x80x94C1-C8alkyl, xe2x80x94E-phenyl, wherein phenyl can be substituted up to three times with C1-C8alkyl, halogen, C1-C8alkoxy, diphenylamino, xe2x80x94CHxe2x95x90CHxe2x80x94Q2, wherein Q2 stands for phenyl, pyridyl, or thiophenyl, which can be substituted up to three times with C1-C8alkyl, halogen, C1-C8alkoxy, xe2x80x94CN, wherein E stands for oxygen or sulfur, and wherein R21 stands for C1-C8alkyl, phenyl, which can be substituted up to three times with C1-C4alkyl, C1-C4alkoxy, or dimethylamino, and R22 and R23 independently from each other stand for hydrogen, R21, C1-C8alkoxy, or dimethylamino, or xe2x80x94NR4R5, wherein R4 and R5, independently from each other stand for hydrogen, phenyl, or C1-C8alkyl-carbonyl, or xe2x80x94NR4R5 stands for a five- or six-membered ring system, and R3 stands for allyl, 
wherein Q3 stands for hydrogen, halogen, C1-C8alkoxy, C1-C8alkyl-amido, unsubstituted or substituted C1-C8alkyl, unsubstituted or up to three times with halogen, xe2x80x94NH2, xe2x80x94OH, or C1-C8alkyl substituted phenyl, and Z stands for a di- or trivalent radical selected from the group consisting of substituted or unsubstituted cyclohexylene, preferably 1,4-cyclohexylene, triazin-2,4,6-triyl, C1-C6alkylene, 1,5-naphthylene, 
wherein
Z1, Z2 and Z3, independently from each other stand for cyclohexylene or up to three times with C1-C4alkyl substituted or unsubstituted phenylene, preferably unsubstituted or substituted 1,4-phenylene,
and wherein R6 and R7, independently from each other, stand for 
n stands for 1, 2 or 3, and m stands for 1 or 2, with the proviso, that R1 and R2 not simultaneously stand for phenyl,
and its different uses such as in electroluminescent devices and as void detection compounds.
Compounds which are both, fluorescent and photostabile, are rare. This is mainly because fluorescence and photostability are usually incompatible with each other. The majority of fluorescent materials obtained to date are compositions employing fluorescent dyes, showing advantages of strong fluorescence, however, at the same time poor lightfastness, too. Hence, the known fluorescent materials are applied for only limited applications, e.g. interior uses, i.e. almost no uses are known for applications where high lightfastness is required.
In particular, perylene based compounds (especially compounds of the known LUMOGEN(copyright) series from BASF) for highly photostabile and fluorescent compounds are used by dissolving it into media such as plastics to give fluorescent compositions. However, their solubility is insufficient thereby failing in obtaining strong color strength of the corresponding compositions.
Further, EP-A 456,609 discloses the preparation and use of a benzoimidazoisoindolone as a highly photostabile and fluorescent pigment. However, this pigment exhibits only a weak solid-state fluorescence and a weak reflection color. In addition, the obtained color range is limited to only greenish yellow to yellow. Another disadvantage is that a kind of benzoimidazoisoindolone irritates the skin and crystal growth is too fast in a polymer matrix.
Also used are coumarin and rhodamine dyes dispersed in a plastic matrix (so-called fluorescent pigments). However, their photostability is poor.
Some maleimide derivatives are well-known compounds. E.g. J.Org.Chem. 42 (1977) 2819-2825 describes 1,2-diphenylmaleyl derivatives such as 1,2-diphenylmaleyl-N-cyclohexylimide as a protecting group for amino functions. Although it is mentioned that these compounds are yellow and fluorescent, no examples and no evaluation is given with regard to fluorescence properties and photostabilities.
Tetrahedron 51 (1995) 9941-9946 describe the synthesis of the marine alkaloid polycitrin, another red, fluorescent 1,2-diphenylmaleyl derivative, and intermediates thereof. However, the object of this work is not to show ways to enhance fluorescent properties and photostability of maleimide derivatives.
U.S. Pat. No. 4,596,867 describes the preparation of disubstituted maleic anhydride compounds. On col. 5 it is speculated that the imides of this compounds with amines such as t-butylaniline or octadecylamine can yield soluble compounds useful as fluorescent dyes and markers. However, no examples or other hints are given to support this statement. Rather, examples are directed to the preparation of polyimides in which the claimed anhydrides are reacted with diamines. In addition, there is no teaching of how to increase the photostability of fluorescent maleimide compounds.
Chem. Pharm. Bull. 28(7) (1980) 2178-2184 describes, too, diphenylmaleimides of the formula 
wherein R8 stands for xe2x80x94CH2Ph, xe2x80x94CH2CH2CH3, xe2x80x94CH(CH3)2, and xe2x80x94CH2CH(CH3)2. Although the compounds are described as yellow fluorescent compounds nothing is mentioned concerning increasing the properties of photostability and fluorescence.
JP-A2 50123664 describes a method for the preparation of 
wherein R stands for C1-C4alkyl, phenyl or tolyl, and Ar stands for phenyl or tolyl. Explicitly, two compounds are prepared wherein Ar stands for phenyl, and R for n-butyl and phenyl, resp. However, nothing is mentioned about fluorescence and photostability. Rather, it is speculated that this compounds are usable as medical drugs, pesticides and starting materials thereof.
Chem. Ber. 26 (1893) 2479 describes the preparation of 3,4,3xe2x80x2,4xe2x80x2-tetraphenyl-1,1xe2x80x2ethandiyl-bis-pyrrole-2,5-dione. However, nothing is known with regard to photostability, fluorescence, and its uses inter alia in electroluminescent devices.
EP-A 628,588 describes the use of bismaleimides, especially 
to increase the molecular weight of polyamides. However, no teaching is given with regard to the photostability and fluorescence of the mentioned compounds and other uses.
Hence, the object of the present invention was to provide photostabile fluorescent compounds, preferably exhibiting a high photostability and a strong solid-state and/or molecular state fluorescence. Further, another object is to broaden the range of available colors within this field, preferably strong reflection colors, combined with the abovementioned properties.
In addition, the provided compounds should be usable in electroluminescent devices as light-emitting substances, as void detection compounds, as inks for security printings, emitters for scintilators, light absorbers for solar collectors, light converters for agriculture etc.
Especially, fluorescent compounds should be provided which, compared to optical brighteners, have a superior solubility thus making an incorporation into paints and lacquers more easy. In addition, the fluorescent compounds should show fluorescence in the solid state, a superior photostability with no or only minimal products leading to discoloration of e.g. white coatings, a lesser migration, a lesser contamination of the working environment, fluorescence should be observed only at voids and not at the whole surface yielding a better contrast compared to e.g. optical brighteners and allowing the detection of minor defects or damages. Further, the fluorescent compounds should be useful in dark and white pigmented systems in which optical brighteners fail. Finally, fluorescent compounds with a superior photostability should be provided allowing long-term void detection, i.e. an inspection after months or maybe years after the application.
Accordingly, the aforementioned fluorescent maleimides were found. In addition, novel compounds, their preparation and uses of the provided compounds such as in electroluminescent devices and as void detection compounds were found, too.
A preferred embodiment of the present invention relates to fluorescent maleimides of the formula II 
wherein R9 has the meaning of R1, and R10 stands for R3.
Another preferred embodiment of the present invention relates to fluorescent maleimides of the formula III 
wherein R11 stands for R1, and R12 stands for R2, wherein R11 and R12 do no stand simultaneously for the same substituent, R13 stands for R3.
Another preferred embodiment of the present invention relates to fluorescent maleimides of the formula IV 
wherein R13, R14, R16 and R17 independently from each other stand for the radicals as defined under R1, and R15 stands for a single bond, or a divalent radical, preferably selected from the group consisting of substituted or unsubstituted cyclohexylen, preferably 1,4-cyclohexylene, C1-C4alkylene, 1,5-naphthylene, 
particularly preferred R15 stands for a single bond, 2,5-di-tert.-butyl-1,4-phenylene, 1,2-ethylene, 1,5-naphthylene, 2,5-dimethyl-1,4-phenylene, 4,5-dimethyl-1,4-phenylene, trans-1,4-cyclohexylene, 
Particularly preferred inventive compounds are the following compounds: 
C1-C8alkyl is typically linear or branchedxe2x80x94where possiblexe2x80x94methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, tert.-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 1,1,3,3-tetramethylbutyl and 2-ethylhexyl, more preferably C1-C4alkyl such as typically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, tert.-butyl.
C1-C6alkylene is typically methylene, 1,1-, 1,2-ethylene, 1,3-propylene, 1,4-butylene, 1,5-pentylene, 1,6-hexylene.
C1-C8alkoxy is typically methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec.-butoxy, isobutoxy, tert.-butoxy, n-pentoxy, 2-pentoxy, 3-pentoxy, 2,2-dimethylpropoxy, n-hexoxy, n-heptoxy, n-octoxy, 1,1,3,3-tetramethylbutoxy and 2-ethylhexoxy, preferably C1-C4alkoxy such as typically methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec.-butoxy, isobutoxy, tert.-butoxy.
Halogen stands for fluoro, chloro, bromo or iodo, preferably for chloro or bromo.
C1-C8alkyl-carbonyl is typically methyl-carbonyl (=acetyl), ethyl-carbonyl, n-propyl-carbonyl, isopropyl-carbonyl, n-butyl-carbonyl, sec.-butyl-carbonyl, isobutyl-carbonyl, tert.-butyl-carbonyl, n-pentyl-carbonyl, 2-pentyl-carbonyl, 3-pentyl-carbonyl, 2,2-dimethylpropyl-carbonyl, n-hexyl-carbonyl, n-heptyl-carbonyl, n-octyl-carbonyl, 1,1,3,3-tetramethylbutyl-carbonyl and 2-ethylhexyl-carbonyl, more preferably C1-C4alkyl-carbonyl such as typically methyl-carbonyl, ethyl-carbonyl, n-propyl-carbonyl, isopropyl-carbonyl, n-butyl-carbonyl, sec.-butyl-carbonyl, isobutyl-carbonyl, tert.-butyl-carbonyl.
C1-C8alkyl-amido is typically acetamido, ethaneamido, n-propaneamido, isopropaneamido, n-butane-amido, sec.-butane-amido, isobutane-amido, tert.-butane-amido, n-pentane-amido, 2-pentane-amido, 3-pentane-amido, 2,2-dimethylpropane-amido, n-hexane-amido, n-heptane-amido, n-octane-amido, 1,1,3,3-tetramethylbutane-amido and 2-ethylhexane-amido, more preferably C1-C4alkane-amido such as typically acetamido, ethaneamido, n-propaneamido, isopropaneamido, n-butaneamido, sec.-butaneamido, isobutaneamido, tert.-butaneamido.
If xe2x80x94NR4R5 stand for a five- or six-membered ring system, the following ring systems are preferred: 4-morpholinyl (=morpholino),1-indolinyl, 1- or 2-piperidyl, 1-piperazinyl, 1-indolinyl, 2-isoindolinyl, 1-quinuclidinyl, 1-pyrrolidinyl, and 9-carbazolyl.
The inventive maleyl derivatives I to IV can be synthesized starting from the corresponding maleic anhydrides and amines in analogy to methods well known in the art such as described in Tetrahedron Letters 31(36) (1990) 5201-5204, J.Org.Chem. 42 (17) (1977) 2819-2825, Chem. Pharm. Bull. 28(7) (1980) 2178-2184, or by methods described in Tetrahedron 51(36) (1995) 9941-9946 or JP-A2 50123664.
In a preferred embodiment the corresponding diarylmaleic anhydride of the formula V 
wherein R18 and R19, independently from each other stand for R1 or R2, is reacted with an amine H2Nxe2x80x94R3 or diamine H2Nxe2x80x94Zxe2x80x94NH2.
The corresponding maleic anhydrides are known or can be prepared in analogy to known methods e.g. as described in J.Org.Chem. 55 (1990) 5165-5170 or U.S. Pat. No. 4,596,867, or as described in detail below. Amines H2Nxe2x80x94R3 and diamines H2Nxe2x80x94Zxe2x80x94NH2 are also known and commercially available from chemical suppliers.
Usually the molar ratio of anhydride V to amine H2Nxe2x80x94R3 is chosen in the range of from 0.1:1 to 2:1. Usually the molar ratio of anhydride V to diamine H2Nxe2x80x94Zxe2x80x94NH2 is chosen in the range of from 0.5:1 to 5:1.
Preferably, the reaction is carried out in the presence of a solvent, wherein the amount of solvent usually is chosen in the range of from 5 to 50 weight-%, related to the diarylmaleic anhydride V.
As solvents usual organic solvents such as acetic acid, toluene, dimethylformamide or a mixture thereof can be chosen.
The reaction temperature preferably is chosen in the range of from 80 to 150, more preferred from 100 to 120xc2x0C. The reaction timexe2x80x94usually depending from the chosen reaction temperaturexe2x80x94preferably is chosen in the range of from 2 to 20 hours.
After removal of the solvent, the product can be purified by known methods if desired, e.g. by chromatography, or crystallization.
If so-called unsymmetrical maleimides I or IV are desired, i.e. R3 stands for e.g. 
wherein R6 and R7 stand for a substituent as described for R1 and R2, but are different from the chosen R1 and R2, or in formula IV R13 and R14 are different from R16 and R17, then it is preferred to add small amounts of anhydride V to a surplus of diamine H2N Z NH2, isolate the obtained product Va 
and react this amine Va with another anhydride V, in which the aryl substituents, e.g. R6 and R7 or R16 or R17, are chosen differently from R18 and R19. Of course other possibilities shall not be excluded, e.g. if one amino group of the diamine is protected etc.
Another preferred embodiment relates to a process for the preparation of maleimides I, wherein in a first step the diarylmaleic anhydride V is reacted with ammonium acetate to yield the intermediate Vb 
Intermediate Vb then is reacted with a base, and the obtained anion in a subsequent step with a halogen compound Xxe2x80x94R3 or Xxe2x80x94Zxe2x80x94X to yield a desired product according to formula 1.
Usually, the molar ratio of diarylmaleic anhydride V to ammonium acetate is chosen in the range of from 0.01:1 to 0.5:1, preferably from 0.05:1 to 0.15:1.
Preferably, the reaction temperature is chosen in the range of from 80 to 130xc2x0 C., more preferably under reflux conditions of the reaction mixture.
It is preferred, too, to carry out the reaction in a solvent. The amount of solvent preferably is chosen in the range of from 10 to 100 weight-%, related to the amount of diarylmaleic anhydride V.
As solvent usual organic solvents such as toluene, DMF, or a mixture thereof, or acetic acid, preferably acetic acid can be used.
Generally, the reaction time is chosen in the range of from three to 20 hours. The desired intermediate Vb can be worked up in usual ways such as filtering, washing, andxe2x80x94if desiredxe2x80x94further purification by chromatography.
The molar ratio of the base and intermediate Vb preferably is chosen in the range of from 1:1 to 5:1.
As a base an alkali metal alkoxide, an alkali metal hydride such as potassium tert.-butoxide, sodium hydride or potassium hydride, preferably sodium hydride, can be used.
Preferably, the reaction with the base is carried out in the presence of a solvent. The amount of solvent can be chosen in the range of from 5 to 100 weight-%, related to intermediate Vb. As solvent usual organic solvents such as N-methylpyrrolidone (xe2x80x9cNMPxe2x80x9d), or dimethyl formamide (xe2x80x9cDMFxe2x80x9d), preferably DMF, can be used.
The reaction temperature usually is chosen in the range of from 20 to 80xc2x0 C., preferably room temperature.
The reaction time usually is chosen in the range of from 0.5 to 5 hours.
Preferably, the reaction mixture is not worked up.
Then, halogen compound Xxe2x80x94R3 or Xxe2x80x94Zxe2x80x94X is added to the obtained reaction mixture. Usually, the molar ratio of Xxe2x80x94R3 or Xxe2x80x94Zxe2x80x94X to intermediate Vb is chosen in the range of from 1:1 to 10:1.
The reaction temperature usually is chosen in the range of from 20 to 120xc2x0 C., preferably room temperature.
The reaction time usually is chosen in the range of from 0.5 to 10 hours.
After adding water to the reaction mixture, usually 0.5 to 10 times in volume related to the amount of solvent, if desired, the obtained diarylmaleimide can be worked up in usual ways such as extraction and/or chromatography.
Another preferred embodiment relates to a process for the preparation of diarylmaleic anhydrides V in which a glyoxylic acid derivative VI 
is treated with a base and, subsequently, the thus obtained salt VIa is reacted with a carboxylic acid VII 
wherein (a) R18 stands for R1 and R19 for R1 or R2, or (b) R18 stands for R2 and R19 for R1.
Usually, the molar ratio of the base to glyoxylic acid derivative VI is chosen in the range of from 1:1 to 20:1, preferably from 1.5:1 to 3:1.
As a rule, the temperature during the formation of the salt VIa is chosen in the range of from 50 to 110, preferably from 70 to 80xc2x0 C.
Preferably, the salt-formation of VIa is carried out in the presence of an aliphatic alcohol such as C1-C4alkanols such as methanol, ethanol, n-, i-propanol, n-, iso-, sek.-, tert.-butanol. The amount of solvent usually is chosen in the range of from 3 to 100, based on the amount of glyoxylic acid derivative VI.
As a base preferably alkoxides such as alkali metal alkoxides, more preferably alkali metal salts of C1-C4alkanols such as sodium methanoate, potassium methanoate, sodium acetate, potassium acetate, sodium n-propanoate, potassium n-propanoate, sodium n-, iso-, sek.-, tert. butanoate, potassium n-, iso-, sek.-, tert.-butanoate, preferably potassium tert.-butanoate, can be used.
Usually, the reaction time is chosen in the range of from 0.5 to 5 hours.
As a rule, the obtained salt VIa is separated from the reaction mixture, preferably followed by removal of the solvent and drying over in an atmosphere under reduced pressure.
In the second step of the above process the salt VIa is mixed with the carboxylic acid VII usually in the presence of acetic anhydride at a temperature in the range of from 80 to 140xc2x0 C., preferably under reflux conditions of the reaction mixture.
In general, the molar ratio of glyoxylic acid salt derivative VIa to carboxylic acid VII is chosen preferably in the range of from 5:1 to 0.2:1, preferably from 0.8:1 to 1.2:1.
Generally, the amount of acetic anhydride to the amount of glyoxylic acid salt derivative VIa is chosen preferably in the range of from 0.05:1 to 1:1, preferably from 0.1:1 to 0.2:1.
Usually, the reaction time of this second step is chosen in the range of from 0.5 to 10, preferably from one to three hours.
The isolation of the product can be carried out by known methods in the art, e.g. removing of acetic anhydride by distillation, preferably under an atmosphere of reduced pressure, followed by washing the product with appropriate organic solvents such as acetone or ethyl acetate or by crystallization or chromatography etc.
The carboxylic acid VII can be obtained by reducing the glyoxylic acid derivative VI with a reducing agent such as hydrazine under basic conditions.
In a preferred embodiment the glyoxylic acid derivative VI is treated with hydrazine or hydrazine monohydrate in a temperature range of from 70 to 120xc2x0 C., preferably under reflux conditions, usually for 0.2 to 2 hours. Thereafter, a base such as a alkali metal or earth alkaline metal hydroxide such as sodium hydroxide or potassium hydroxide is added to the reaction mixture after cooling down to a temperature in the range of from 80 to 100, preferably from 95 to 100xc2x0 C., and then heated to a temperature range of from 100 to 120xc2x0 C., preferably under reflux conditions for 2 to 10 hours. Afterwards, the hydrazine is removed e.g. by distillation, and the thus obtained reaction mixture preferably is acidified with a mineral acid such as hydrochloric acid, sulfuric acid, nitric acid, preferably hydrochloric acid, to a pH in the range of from 2 to 4. After that the product can be isolated e.g. by extraction with an appropriate solvent such as methylene chloride, followed e.g. by crystallization or column chromatography.
The molar ratio of hydrazine to glyoxylic acid derivative VI usually is chosen in the range of from 2:1 to 20:1, preferably from 5:1 to 10:1.
The amount of the base usually is chosen in the range of from 2 to 10, preferably from 3 to 5 weight-%, related to glyoxylic acid derivative VI.
The glyoxylic acid derivative VI can be obtained by saponification of ester VIII 
wherein R20 stands for C1-C4alkyl, in analogy to known methods.
Preferably, ester VIII is treated with a base such as an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide, and the like in the presence of a polar solvent such as an C1-C4alkanol or an aqueous solution thereof. In a preferred embodiment the saponification is carried out in the presence of a mixture of water and an alkanol R20OH in a volume ratio of 5:1 to 0.5:1. Further it is preferred to carry out the saponification at an elevated temperature, such as in the range of from 70 to 100xc2x0 C., preferably under reflux conditions at ambient pressure.
The reaction time mainly depends on the reactivity of the educts and the chosen temperature. E.g. under reflux conditions the reaction time usually is chosen in the range of from one five hours.
After that, the reaction mixture usually is acidified with an acid to a pH range of from 2 to 4. As an acid mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, preferably hydrochloric acid, can be used.
Generally, the desired glyoxylic acid derivative VII is isolated from the reaction mixture by known methods such as extraction, crystallization, chromatography, preferably extraction.
The starting material, ester VIII, can be prepared by treating the aryl compound with the halogen glyoxylate X 
wherein X stands for a halogen, preferably for chlorine or bromine, in the presence of AIX3 and a solvent.
In a preferred embodiment, a mixture of AIX3 in a solvent such as methylene chloride is added portionwise, preferably dropwise, to a mixture of compounds IX and X.
Usually, the molar ratio of aryl compound IX to halogen glyoxylate X is chosen in the range of from 0.5:1 to 5:1, preferably from 0.8:1 to 2:1.
The amount of AIX3 preferably is chosen in the range of from 1 to 2 weight-%, related to the amount of glyoxylate X.
During the addition of AIX3 to the mixture of compound IX and glyoxylate X, the reaction temperature is chosen preferably in the range of from xe2x88x9210 to 20, more preferably from 0 to 5xc2x0 C. After the addition the reaction temperature usually is chosen in the range of from 10 to 40xc2x0 C., the preferred temperature is room temperature.
The reaction time generally is in the range of from 3 to 20 hours.
Thereafter, the reaction mixture preferably is treated with water, preferably ice and acidified to a pH in the range of from 2 to 4 with one of the above mentioned mineral acids, preferably diluted hydrochloric acid. The isolation of he product can be carried out with methods well known in the art such as extraction with dichloromethane or diethylether. If desired the ester II can be further purified e.g. by chromatography.
Other compounds such as the intermediate 
can be prepared in analogy to the abovementioned process.
Another embodiment of the present invention relates to the use of the claimed maleimides as well for all other fluorescent maleimides according to the general formula given in this application or mentioned in the examples for scintillator films for the detection of atomic and nuclear radiation. In their simplest form these detectors usually consist of a polymer matrix, such as polystyrene, containing low concentrations of a fluorescent maleimide as fluorophore or an energy donor/acceptor mixture containing a fluorescent maleimide as a key component.
Another embodiment of the present invention relates to the use of the claimed fluorescent maleimides or those known compounds mentioned additionally in the examples for the preparation and use of luminescent solar energy collectors. The operation of a luminescent solar concentrator usually is based on the absorption of solar radiation in a collector containing a fluorescent species in which the emission bands have little or no overlap with the absorption bands. Generally, the fluorescence emission is trapped by total internal reflection and concentrated at the edges of a collector, which is usually a thin flat plate, to the edge of which a p-n junction photovoltaic ribbon is fixed and the light energy converted to electrical energy. Luminescent solar collectors usually can collect both direct and diffuse light, and there is a good heat dissipation of non-utilized energy. Tracking of the sun usually is unnecessary and fluorescent species can be selected to allow matching if the concentrated light to the maximum sensitivity of the photovoltaic cell.
A further embodiment of this invention relates to the use of the claimed fluorescent maleimides or those known compounds mentioned additionally in the examples for the preparation and use of printing inks such as gravure, flexo and off-set inks preferably for publication, packagings and laminations, as well as non-impact printings such as ink jet printing inks and electrophotographic toners for printers and copy machines. The maleimides can be applied in the usual method known in the art. The inks can be used also in a way known in the art for functional inks as well as for security printings for banknotes and indicators.
Another embodiment of the present invention is related to a method of coloring high molecular organic materials (having a molecular weight usually in the range of from 103 to 107 g/mol) by incorporating the inventive fluorescent compounds by known methods in the art.
As high molecular weight organic materials the following can be used such as biopolymers, and plastic materials, including fibres.
The present invention relates preferably to the use of the inventive maleimides I for the preparation of
inks, for printing inks in printing processes, for flexographic printing, screen printing, packaging printing, security ink printing, intaglio printing or offset printing, for pre-press stages and for textile printing, for office, home applications or graphics applications, such as for paper goods, for example, for ballpoint pens, felt tips, fiber tips, card, wood, (wood) stains, metal, inking pads or inks for impact printing processes (with impact-pressure ink ribbons), for the preparation of
colorants, for coating materials, for industrial or commercial use, for textile decoration and industrial marking, for roller coatings or powder coatings or for automotive finishes, for high-solids (low-solvent), water-containing or metallic coating materials or for pigmented formulations for aqueous paints, for the preparation of
pigmented plastics for coatings, fibers, platters or mold carriers, for the preparation of
non-impact-printing material for digital printing, for the thermal wax transfer printing process, the ink jet printing process or for the thermal transfer printing process, and also for the preparation of
color filters, especially for visible light in the range from 400 to 700 nm, for liquid-crystal displays (LCDs) or charge combined devices (CCDs) or for the preparation of
cosmetics or for the preparation of
polymeric ink particles, toners, dry copy toners liquid copy toners, or electrophotographic toners, and electroluminescent devices.
Illustrative examples of suitable organic materials of high molecular weight which can be colored with the inventive fluorescent maleimides of this invention are vinyl polymers, for example polystyrene, poly-xcex1-methylstyrene, poly-p-methylstyrene, poly-p-hydroxystyrene, poly-p-hydroxyphenylstyrene, polymethyl methacrylate and polyacrylamide as well as the corresponding methacrylic compounds, polymethylmaleate, polyacrylonitrile, polymethacrylonitrile, polyvinyl chloride, polyvinyl fluoride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl acetate, polymethyl vinyl ether and polybutyl vinyl ether; polymers which are derived from maleinimide and/or maleic anhydride, such as copolymers of maleic anhydride with styrene; polyvinyl pyrrolidone; ABS; ASA; polyamides; polyimides; polyamidimides; polysulfones; polyether sulfones; polyphenylene oxides; polyurethanes; polyureas; polycarbonates; polyarylenes; polyarylene sulfides; polyepoxides; polyolefins such as polyethylene and polypropylene; polyalkadienes; biopolymers and the derivatives thereof e.g. cellulose, cellulose ethers and esters such as ethylcellulose, nitrocellulose, cellulose acetate and cellulose butyrate, starch, chitin, chitosan, gelatin, zein; natural resins; synthetic resins such as alkyd resins, acrylic resins, phenolic resins, epoxide resins, aminoformaldehyde resins such as urea/formaldehyde resins and melamine/formaldehyde resin; vulcanized rubber; casein; silicone and silicone resins; rubber, chlorinated rubber; and also polymers which are used, for example, as binders in paint systems, such as novolaks which are derived from C1-C6-aldehydes such as formaldehyde and acetaldehyde and a binuclear or mononuclear, preferably mononuclear, phenol which, if desired, is substituted by one or two C1-C9alkyl groups, one or two halogen atoms or one phenyl ring, such as o-, m- or p-cresol, xylene, p-tert.-butylphenol, o-, m- or p-nonylphenol, p-chlorophenol or p-phenylphenol, or a compound having more than one phenolic group such as resorcinol, bis(4-hydroxyphenyl)methane or 2,2-bis(4-hydroxyphenyl)propane; as well as suitable mixtures of said materials.
Particularly preferred high molecular weight organic materials, in particular for the preparation of a paint system, a printing ink or ink, are, for example, cellulose ethers and esters, e.g. ethylcellulose, nitrocellulose, cellulose acetate and cellulose butyrate, natural resins or synthetic resins (polymerization or condensation resins) such as aminoplasts, in particular urea/formaldehyde and melamine/formaldehyde resins, alkyd resins, phenolic plastics, poly-carbonates, polyolefins, polystyrene, polyvinyl chloride, polyamides, polyurethanes, poly-ester, ABS, ASA, polyphenylene oxides, vulcanized rubber, casein, silicone and silicone resins as well as their possible mixtures with one another.
It is also possible to use high molecular weight organic materials in dissolved form as film formers, for example boiled linseed oil, nitrocellulose, alkyd resins, phenolic resins, melamine/formaldehyde and urea/formaldehyde resins as well as acrylic resins.
Said high molecular weight organic materials may be obtained singly or in admixture, for example in the form of granules, plastic materials, melts or in the form of solutions, in particular for the preparation of spinning solutions, paint systems, coating materials, inks or printing inks.
In a particularly preferred embodiment of this invention, the inventive fluorescent maleimides I are used for the mass coloration of polyvinyl chloride, polyamides and, especially, polyolefins such as polyethylene and polypropylene as well as for the preparation of paint systems, including powder coatings, inks, printing inks, color filters and coating colors.
Illustrative examples of preferred binders for paint systems are alkyd/melamine resin paints, acryl/melamine resin paints, cellulose acetate/cellulose butyrate paints and two-pack system lacquers based on acrylic resins which are crosslinkable with polyisocyanate.
According to observations made to date, the inventive fluorescent maleimides I can be added in any desired amount to the material to be colored, depending on the end use requirements. In the case of high molecular weight organic materials, for example, the fluorescent maleimides I prepared according to this invention can be used in an amount in the range from 0.01 to 40, preferably from 0.01 to 5% by weight, based on the total weight of the colored high molecular weight organic material.
For the preparation of paints systems, coating materials, color filters, inks and printing inks, the corresponding high molecular weight organic materials, such as binders, synthetic resin dispersions etc. and the inventive fluorescent maleimides I are usually dispersed or dissolved together, if desired together with customary additives such as dispersants, fillers, paint auxiliaries, siccatives, plasticizers and/or additional pigments or pigment precursors, in a common solvent or mixture of solvents. This can be achieved by dispersing or dissolving the individual components by themselves, or also several components together, and only then bringing all components together, or by adding everything together at once.
Hence, a further embodiment of the present invention relates to a method of using the inventive fluorescent maleimides I for the preparation of dispersions and the corresponding dispersions, and paint systems, coating materials, color filters, inks and printing inks comprising the inventive fluorescent maleimides I.
A particular embodiment of this invention concerns ink jet inks comprising the inventive fluorescent compositions. The desired ink may contain up to 30% by weight of the fluorescent composition, but will generally be in the range of 0.1 to 10, preferably from 0.1 to 8% by weight of the total ink composition for most thermal ink jet printing applications.
Further, the inks usually contain polymeric dispersants such as random, block, branched or graft polymers or copolymers. Most preferred are polymeric dispersants made by the group transfer polymerization process, because in general these are free from higher molecular weight species that tend to plug pen nozzles.
Representative compounds useful for this purpose include e.g. polymers of polyvinyl alcohol, cellulosics and ethylene oxide modified polymers, and dispersant compounds containing ionisable groups such as acrylic acid, maleic acid or sulfonic acid.
The polymeric dispersant is generally present in an amount in the range of from 0.1 to 30, preferably from 0,1 to 8% by weight of the total ink composition.
In addition to, or in place of the preferred polymeric dispersants, surfactants may be used as dispersants. These may be anionic, nonionic, or amphoteric surfactants. A detailed list of non-polymeric as well as some polymeric dispersants is disclosed in the section on dispersants of Manufacturing Confection Publishing Co., (1990) p. 110-129, McCutcheon""s Functional Materials, North America Edition.
Usually the ink contains an aqueous medium such as water or a mixture of water and at least one water-soluble organic solvent. Water-soluble organic solvents are well known, representative examples of which are disclosed in e.g. U.S. Pat. No. 5,085,698. Selection of a suitable mixture of water and water-soluble organic solvent depends on usually requirements of the specific application such as desired surface tension and viscosity, drying time of the ink, and the media substrate onto which the ink will be printed.
Particularly preferred is a mixture of a water-soluble solvent having at least two hydroxyl groups, e.g. diethylene glycol, and water, especially deionized water.
In the event that a mixture of water and a water-soluble organic solvent is used as aqueous medium, water usually would comprise from 30 to 95, preferably 60 to 95% by weight, based on the total weight of the aqueous medium.
The amount of aqueous medium generally is in the range of from 70 to 99.8, preferably from 84 to 99.8%, based on the total weight of the ink.
The ink may contain other ingredients well known to those skilled in the art such as surfactants to alter surface tension as well as to maximize penetration. However, because surfactants may destabilize dispersions, care should be taken to insure compatibility of the surfactant with the other ink components. In general, in aqueous inks, the surfactants may be present in amounts ranging from 0.01 to 5, preferably from 0.2 to 3% by weight, based on the total weight of the ink.
Biocides may be used in the ink compositions to inhibit growth of microorganisms. Sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities. Other known additives, such as viscosity modifiers may also be added.
A further embodiment concerns the use of the inventive fluorescent compounds I in phase change ink jet inks. The preparation of such inks is well known in the art, e.g. described in detail in EP-A 816,410.
For the pigmentation of high molecular weight organic material, the inventive maleimides I, optionally in the form of masterbatches, usually are mixed with the high molecular weight organic materials using roll mills, mixing apparatus or grinding apparatus. Generally, the pigmented material is subsequently brought into the desired final form by conventional processes, such as calandering, compression molding, extrusion, spreading, casting or injection molding. In order to prepare non-rigid moldings or to reduce their brittleness it is often desired to incorporate so-called plasticizers into the high molecular weight organic materials prior to forming. Examples of compounds which can be used as such plasticizers are esters of phosphoric acid, phthalic acid or sebacic acid. The plasticizers can be added before or after the incorporation of the inventive maleimides I into the polymers. It is also possible, in order to achieve different hues, to add fillers or other coloring constituents such as white, color or black pigments in desired amounts to the high molecular weight organic materials in addition to the inventive maleimides I.
For pigmenting lacquers, coating materials and printing inks the high molecular weight organic materials and the inventive maleimides I, alone or together with additives, such as fillers, other pigments, siccatives or plasticizers, are generally dissolved or dispersed in a common organic solvent or solvent mixture. In this case it is possible to adopt a procedure whereby the individual components are dispersed or dissolved individually or else two or more are dispersed or dissolved together and only then are all of the components combined.
The present invention additionally relates to inks comprising a coloristically effective amount of the pigment dispersion of the inventive maleimides I.
Processes for producing inks especially for ink jet printing are generally known and are described for example in U.S. Pat. No. 5,106,412.
The inks can be prepared, for example, by mixing the pigment dispersions comprising the inventive maleimides I with polymeric dispersants.
The mixing of the pigment dispersions with the polymeric dispersant takes place preferably in accordance with generally known methods of mixing, such as stirring or mechanical mixing; it is preferably advisable to use intensive mechanical mixers such as the so-called ULTRATURAX(copyright) stirrer from Kunkel and Jahn, Staufen (Germany).
When mixing a maleimide I with polymeric dispersants it is preferred to use a water-dilutable organic solvent.
The weight ratio of the pigment dispersion to the ink in general is chosen in the range of from 0.001 to 75% by weight, preferably from 0.01 to 50% by weight, based on the overall weight of the ink.
Examples of suitable polymeric dispersants are carboxyl-containing polyacrylic resins such as polymeric methacrylic or crotonic acids, especially those obtained by addition polymerization of acrylic acid or acrylic acid and other acrylic monomers such as acrylates. Depending on the field of use or when using maleimides I, it is also possible, if desired, to admix a small proportion of a water-miscible organic solvent in from 0.01 to 30% by weight, based on the overall weight of the ink, and/or to admix water and/or bases so as to give a pH in the range from 7 to 11. It may likewise be advantageous to add preservatives, antifoams, surfactants, light stabilizers and pH regulators, for example, to the ink of the invention, depending on the field of use.
Examples of suitable pH regulators are inorganic salts such as lithium hydroxide or lithium carbonate, quaternary ammonium hydroxide or ammonium carbonate. Examples of preservatives and antifoams are, for example, sodium dehydroacetate, 2,2-dimethyl-6-acetoxydioxane or ammonium thioglycolate. It is also possible to employ known agents which regulate the viscosity or the surface tension and are described in e.g. U.S. Pat. No. 5,085,698.
Examples of water-miscible organic solvents are aliphatic C1-C4alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert.-butanol, ketones such as acetone methyl ethyl ketone, methyl isobutyl ketone or diacetone alcohol, and also polyols, Cellosolves(copyright) and carbitols, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, propylene gylcol, ethylene glycol monomethyl or monoethyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, diethylene glycol monomethyl or monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl or monoethyl ether, and also N-methyl-2-pyrrolidone, 2-pyrrolidone, N,Nxe2x80x2-dimethylformamide or N,Nxe2x80x2-dimethylacetamide.
If desired, the ink prepared as described above can be worked up further. The working up of the ink can be carried out by the customary methods for working up dispersions, by separation techniques, such as sieving or centrifuging the coarse particles from the resulting dispersion. It has been found advantageous, too, to carry out centrifuging in two stages of different intensity, e.g. centrifuging in a first step for from ten minutes to one hour at from 2000 to 4000 rpm and then, in a second step, for from 10 minutes to one hour at from 6000 to 10000 rpm.
Following centrifuging or sieving, the dispersion usually can be used directly as an ink for ink jet printing, for example.
The present invention additionally relates to a process for producing color filters comprising a transparent substrate and applied thereon a red, blue and green layer in any desired sequence, by using a red compound I and known blue and green compounds. The different colored layers preferably exhibit patterns such that over at least 5% of their respective surface they do not overlap and with very particular preference do not overlap at all.
The preparation and use of color filters or color-pigmented high molecular weight organic materials are well-known in the art and described e.g. in Displays 14/2, 1151 (1993), EP-A 784085, or GB-A 2,310,072.
The color filters can be coated for example using inks, especially printing inks, which can comprise pigment dispersions comprising the inventive maleimides I or can be prepared for example by mixing a pigment dispersion comprising a maleimides I with chemically, thermally or photolytically structurable high molecular weight organic material (so-called resist). The subsequent preparation can be carried out, for example, in analogy to EP-A 654 711 by application to a substrate, such as a LCD, subsequent photostructuring and development.
Particular preference for the production of color filters is given to pigment dispersions comprising a maleimides I which possess non-aqueous solvents or dispersion media for polymers.
The present invention relates, moreover, to toners comprising a pigment dispersion containing a maleimide I or a high molecular weight organic material pigmented with a maleimide I in a coloristically effective amount.
In a particular embodiment of the process of the invention, toners, coating materials, inks or colored plastics are prepared by processing masterbatches of toners, coating materials, inks or colored plastics in roll mills, mixing apparatus or grinding apparatus.
The present invention additionally relates to colorants, colored plastics, polymeric ink particles, or non-impact-printing material comprising an inventive maleimide I pigment, preferably in the form of a dispersion, or a high molecular weight organic material pigmented with a maleimide I in a coloristically effective amount.
A coloristically effective amount of the pigment dispersion according to this invention comprising an inventive maleimide I denotes in general from 0.0001 to 99.99% by weight, preferably from 0.001 to 50% by weight and, with particular preference, from 0.01 to 50% by weight, based on the overall weight of the material pigmented therewith.
Further, the inventive compounds I can be used for textile application and for the dying of paper.
A further embodiment of the present invention relates to the use of the fluorescent maleimides of the general formula I and of the formula Ia 
for the preparation of and use in organic electroluminescent (xe2x80x9cELxe2x80x9d) devices. Such EL devices are well-known in the art (e.g. described in Appl. Phys. Lett. 51 (1987) 913).
In a preferred embodiment EL devices are used which have the following compositions:
(i) an anode/a hole transporting layer/an electron transporting layer/a cathode in which the inventive compounds I or compounds Ia are used either as positive-hole transport compounds, which is exploited to form the light emitting and hole transporting layers, or as electron transport compounds, which can be exploited to form the light-emitting and electron transporting layers, and
(ii) an anode/a hole transporting layer/a light-emitting layer/an electron transporting layer/a cathode, in which the inventive compounds I or compounds Ia form the light-emitting layer regardless of whether they exhibit positive-hole or electron transport properties in this constitution. It is possible that the light emitting layer can consist of two or more fluorescent substances of formulae I or Ia for energy donor(s) and energy acceptor(s).
The devices can be prepared in several well-known ways. Generally, vacuum evaporation is extensively used for the preparation. The devices can be prepared in several ways. Usually, vacuum evaporation is extensively used for the preparation. Preferably, the organic layers are laminated in the above order on a commercially available indium-tin-oxide (xe2x80x9cITOxe2x80x9d) glass substrate held at room temperature, which works as the anode in the constitutions. The membrane thickness is preferably in the range of 1 to 104 nm, more preferably 1 to 5000 nm, more preferably 1 to 103 nm, more preferably 1 to 500 nm. The cathode metal such as Mg/Ag alloy and Li-Al binary system of ca. 200 nm is laminated on the top of the organic layers. The vacuum during the deposition is preferably less than 0.1333 Pa (1xc3x9710xe2x88x923 Torr), more preferably less than 1.333xc3x9710xe2x88x923 Pa (1xc3x9710xe2x88x925 Torr), more preferably less than 1.333xc3x9710xe2x88x924 Pa (1xc3x9710xe2x88x926 Torr).
As anode usual anode materials which possess high work function such as metals like gold, silver, copper, aluminum, indium, iron, zinc, tin, chromium, titanium, vanadium, cobalt, nickel, lead, manganese, tungsten and the like, metallic alloys such as magnesium/copper, magnesium/silver, magnesium/aluminum, aluminum/indium and the like, semiconductors such as Si, Ge, GaAs and the like, metallic oxides such as indium-tin-oxide (xe2x80x9cITOxe2x80x9d), ZnO and the like, metallic compounds such as Cul and the like, and furthermore, electroconducting polymers such polyacetylene, polyaniline, polythiophene, polypyrrole, polyparaphenylene and the like, preferably ITO, most preferably ITO on glass as substrate can be used.
Of these electrode materials, metals, metallic alloys, metallic oxides and metallic compounds can be transformed into electrodes, for example, by means of the sputtering method. In the case of using a metal or a metallic alloy as a material for an electrode, the electrode can be formed also by the vacuum deposition method. In the case of using a metal or a metallic alloy as a material forming an electrode, the electrode can be formed, furthermore, by the chemical plating method (see for example, Handbook of Electrochemistry, pp 383-387, Mazuren, 1985). In the case of using an electroconducting polymer, an electrode can be made by forming it into a film by means of anodic oxidation polymerization method onto a substrate which is previously provided with an electroconducting coating. The thickness of an electrode to be formed on a substrate is not limited to a particular value, but, when the substrate is used as a light emitting plane, the thickness of the electrode is preferably within the range of from 1 nm to 100 nm, more preferably, within the range of from 5 to 50 nm so as to ensure transparency.
In a preferred embodiment ITO is used on a substrate having an ITO film thickness in the range of from 10 nm (100 xc3x85) to 1 xcexc (10000 xc3x85), preferably from 20 nm (200 xc3x85) to 500 nm (5000 xc3x85). Generally, the sheet resistance of the ITO film is chosen in the range of not more than 100 xcexa9/cm2, preferred from not more than 50 xcexa9/cm2.
Such anodes are commercially available e.g. from e.g. Japanese manufacturers such as Geomatech Co. Ltd., Sanyo Vacuum Co. Ltd., Nippon Sheet Glass Co. Ltd.
As substrate either an electroconducting or electrically insulating material can be used. In case of using an electroconducting substrate, a light emitting layer or a positive hole transporting layer is directly formed thereupon, while in case of using an electrically insulating substrate, an electrode is firstly formed thereupon and then a light emitting layer or a positive hole transporting layer is superposed.
The substrate may be either transparent, semi-transparent or opaque. However, in case of using a substrate as an indicating plane, the substrate must be transparent or semi-transparent.
Transparent electrically insulating substrates are, for example, inorganic compounds such as glass, quartz and the like, organic polymeric compounds such as polyethylene, polypropylene, polymethylmethacrylate, polyacrylonitrile, polyester, polycarbonate, polyvinylchloride, polyvinylalcohol, polyvinylacetate and the like. Each of these substrates can be transformed into a transparent electroconducting substrate by providing it with an electrode according to one of the methods described above.
As examples of semi-transparent electrically insulating substrates, there are inorganic compounds such as alumina, YSZ (yttrium stabilized zirconia) and the like, organic polymeric compounds such as polyethylene, polypropylene, polystyrene, epoxy resin and the like. Each of these substrates can be transformed into a semi-transparent electroconducting substrate by providing it with an electrode according to one of the abovementioned methods.
As examples of opaque electroconducting substrates, there are metals such as aluminum, indium, iron, nickel, zinc, tin, chromium, titanium, copper, silver, gold, platinum and the like, various elctroplated metals, metallic alloys such as bronze, stainless steel and the like, semiconductors such as Si, Ge, GaAs, and the like, electroconducting polymers such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyparaphenylene and the like.
A substrate can be obtained by forming one of the above listed substrate materials to a desired dimension. It is preferred that the substrate has a smooth surface. Even if it has a rough surface, however, it will not cause any problem for practical use, provided that it has round unevenness having a curvature of not less than 20 xcexcm. As for the thickness of the substrate, there is no restriction as far as it ensures sufficient mechanical strength.
As cathode usual cathode materials which possess low work function such as alkali metals, earth alkaline metals, group 13 elements, silver, and copper as well as alloys or mixtures thereof such as sodium, lithium, potassium, sodium-potassium alloy, magnesium, magnesium-silver alloy, magnesium-copper alloy, magnesium-aluminum alloy, magnesium-indium alloy, aluminum, aluminumxe2x80x94aluminum oxide alloy, aluminum-lithium alloy, indium, calcium, and materials exemplified in EP-A 499,011 such as electroconducting polymers e.g. polypyrrole, polythiophene, polyaniline, polyacetylene etc., preferably Mg/Ag alloys, or Lixe2x80x94Al compositions can be used.
In a preferred embodiment magnesium-silver alloy or a mixture of magnesium and silver mixture, or lithium-aluminum alloy or a mixture of lithium and aluminum can be used in a film thickness in the range of from 10 nm (100 xc3x85) to 1 xcexcm (10000 xc3x85), preferably from 20 nm (200 xc3x85) to 500 nm (5000 xc3x85).
Such cathodes can be deposited on the foregoing electron transporting layer by known vacuum deposition techniques described above.
In a preferred ambodiment of this invention a light-emitting layer can be used between the hole transporting layer and the electron transporting layer. Usually it is prepared by forming a thin film of a maleimide of formula I on the hole transporting layer.
As methods for forming said thin film, there are, for example, the vacuum deposition method, the spin-coating method, the casting method, the Langmuir-Blodgett (xe2x80x9cLBxe2x80x9d) method and the like. Among these methods, the vacuum deposition method, the spin-coating method and the casting method are particularly preferred in view of ease in operation and cost. In case of forming a thin film using a fluorescent maleimide I by means of the vacuum deposition method, the conditions under which the vacuum deposition is carried out are usually strongly dependent on the properties, shape and crystalline state of the compound. However, optimum conditions can be selected for example within the range of from 100 to 400xc2x0 C. in temperature for the heating boat, xe2x88x92100 to 350xc2x0 C. in substrate temperature, 1.33xc3x97104 Pa (1xc3x97102 Torr) to 1.33xc3x9710xe2x88x924 Pa (1xc3x9710xe2x88x926 Torr) in pressure and 1 pm to 6 nm/sec in deposition rate.
In an organic EL element, the thickness of the light emitting layer thereof is one of the factors determining its light emission properties. For example, if a light emitting layer is not sufficiently thick, a short circuit can occur quite easily between two electrodes sandwiching said light emitting layer, and therefor, no EL emission is obtained. On the other hand, if the light emitting layer is excessively thick, a large potential drop occurs inside the light emitting layer because of its high electrical resistance, so that the threshold voltage for EL emission increases. Accordingly, it is necessary to limit the thickness of an organic light emitting layer within the range of from 5 nm to 5 xcexcm. A preferable thickness is within the range of from 10 nm to 500 nm.
In the case of forming a light emitting layer by using the spin-coating method and the casting method, the coating can be carried out using a solution prepared by dissolving the fluorescent maleimide I in a concentration of from 0.0001 to 90% by weight in an appropriate organic solvent such as benzene, toluene, xylene, tetrahydrofurane, methyltetrahydrofurane, N,N-dimethylformamide, dichloromethane, dimethylsulfoxide and the like. Herein, the higher the concentration of fluorescent maleimide I the thicker the resulting film, while the lower the concentration, the thinner the resulting film. However, if the concentration exceeds 90% by weight, the solution usually is so viscous that it no longer permits forming a smooth and homogenous film. On the other hand, as a rule, if the concentration is less than 0.0001% by weight, the efficiency of forming a film is too low to be economical. Accordingly, a preferred concentration of the fluorescent maleimide I is within the range of from 0.01 to 80% by weight.
In the case of using the above spin-coating or casting method, it is possible to further improve the homogeneity and mechanical strength of the resulting layer by adding a polymer binder in the solution for forming the light emitting layer. In principle, any polymer binder may be used, provided that it is soluble in a solvent in which the fluorescent maleimide I is dissolved.
Examples of such polymer binders are polycarbonate, polyvinylalcohol, polymethacrylate, polymethylmethacrylate, polyester, polyvinylacetate, epoxy resin and the like. A solution for forming a light emitting layer may have any concentrations of the fluorescent maleimide I, of a polymer binder and solvent. However, if the solid content composed of the polymer binder and fluorescent maleimide I exceeds 99% by weight, the fluidity of the solution is usually so low that it is impossible to form a light emitting layer excellent in homogeneity. On the other hand, if the content of fluorescent maleimide I is substantially smaller than that of the polymer binder, in general the electrical resistance of said layer is very large, so that it does not emit light unless a high voltage is applied thereto. Furthermore, since the concentration of fluorescent maleimide I in the layer is small in this case, its light emission efficiency is relatively low. Accordingly, the preferred composition ratio of a polymer binder to fluorescent maleimide I is chosen within the range of from 10:1 to 1:50 by weight, and the solid content composed of both components in the solution is preferably within the range of from 0.01 to 80% by weight, and more preferably, within the range of about 0.1 to 60% by weight.
In the case of forming a light emitting layer by the spin-coating method or casting method, the thickness of said layer may be selected in the same manner as in the case of forming a light emitting layer by the vacuum deposition method. That is, the thickness of the layer preferably is chosen within the range of from 5 nm to 5 xcexcm, and more preferably, within the range of from 10 nm to 500 nm.
As hole-transporting layers known organic hole transporting compounds such as polyvinyl carbazole, 
a triphenylamine derivative (xe2x80x9cTPDxe2x80x9d) compound disclosed in J. Amer. Chem. Soc. 90 (1968) 3925 
wherein Q1 and Q2 each represent a hydrogen atom or a methyl group;
a compound disclosed in J. Appl. Phys. 65(9) (1989) 3610 
a stilbene based compound 
wherein T and T1 stand for an organic rest
a hydrazone based compound 
and the like.
Compounds to be used as a positive hole transporting material are not restricted to the above listed compounds. Any compound having a property of transporting positive holes can be used as a positive hole transporting material such as triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivative, pyrazolone derivatives, phenylene diamine derivatives, arylamine derivatives, amino substituted chalcone derivatives, oxazole derivatives, stilbenylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, copolymers of aniline derivatives, electro-conductive oligomers, particularly thiophene oligomers, porphyrin compounds, aromatic tertiary amine compounds, stilbenyl amine compounds etc.
Particularly, aromatic tertiary amine compounds such as N,N,Nxe2x80x2,Nxe2x80x2-tetraphenyl-4,4xe2x80x2-diaminobiphenyl, N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-4,4xe2x80x2-diaminobiphenyl (TPD), 2,2xe2x80x2-bis(di-p-torylaminophenyl)propane, 1,1xe2x80x2-bis(4-di-torylaminophenyl)-4-phenylcyclohexane, bis(4-dimethylamino-2-methylphenyl)phenylmethane, bis(4-di-p-tolylaminophenyl)phenyl-methane, N, Nxe2x80x2-diphenyl-N,Nxe2x80x2-di(4-methoxyphenyl)-4,4xe2x80x2-diaminobiphenyl, N,N,Nxe2x80x2, Nxe2x80x2-tetraphenyl-4,4xe2x80x2-diaminodiphenylether, 4,4xe2x80x2-bis(diphenylamino)quaterphenyl, N,N,N-tri(p-tolyl)amine, 4-(di-p-tolylamino)-4xe2x80x2-[4-(di-p-tolylamino)stilyl]stilbene, 4-N,N-diphenylamino-(2-diphenylvinyl)benzene, 3-methoxy-4xe2x80x2xe2x80x94N,N-diphenylaminostilbene, N-phenylcarbazole etc.
Furthermore, 4,4xe2x80x2-bis[N-(1-naphtyl)xe2x80x94N-phenylamino]biphenyl disclosed in U.S. Pat. No. 5,061,569, the compounds in which three triphenylamine units are bound to a nitrogen atom like xe2x80x9cstar-burstxe2x80x9d structure e.g. 4,4xe2x80x2,4xe2x80x3-tris[Nxe2x80x94(3-methylphenyl)xe2x80x94N-phenylamino]triphenylamine disclosed in EP-A 508,562.
A positive hole transporting layer can be formed by preparing an organic film containing at least one positive hole transporting material on the anode. The positive hole transporting layer can be formed by the vacuum deposition method, the spin-coating method, the casting method, the LB method and the like. Of these methods, the vacuum deposition method, the spin-coating method and the casting method are particularly preferred in view of ease and cost.
In the case of using the vacuum deposition method, the conditions for deposition may be chosen in the same manner as described for the formation of a light emitting layer (see above). If it is desired to form a positive hole transporting layer comprising more than one positive hole transporting material, the coevaporation method can be employed using the desired compounds.
In the case of forming a positive hole transporting layer by the spin-coating method or the casting method, the layer can be formed under the conditions described for the formation of the light emitting layer (see above).
As in the case of forming a light emitting layer using a solution containing a polymer binder, a smoother and more homogeneous positive hole transporting layer can be formed by using a solution containing a binder and at least one positive hole transporting material. The coating using such a solution can be performed in the same manner as in cases of forming a light emitting layer using a polymer binder. Any polymer binder may be used, provided that it is soluble in a solvent in which at least one positive hole transporting material is dissolved. Examples of appropriate polymer binders and of appropriate and preferred concentrations are given above when describing the formation of a light emitting layer.
The thickness of a positive hole transporting layer is preferably chosen in the range of from 0.5 to 1000 nm, preferably from 1 to 100 nm, more preferably from 2 to 50 nm.
As electron transporting materials for an electron-transporting layer it is preferred to have a high electron injection efficiency from the cathode and a high electron mobility. The following materials can be exemplified for electron transporting materials: tris(8-hydroxyquinolinoato)-aluminum(III) and its derivatives, bis(10-hydroxybenzo[h]quinolinolato)beryllium(II) and its derivatives, oxadiazole derivatives such as 2-(4-biphenyl)-5-(4-tert.-butylphenyl)-1,3,4-oxadiazole and its dimer systems such as 1 ,3-bis(4-tert.-butylphenyl-1,3,4)oxadiazolyl)-biphenylene and 1,3-bis(4-tert.-butylphenyl-1,3,4-oxadiazolyl)phenylene, triazole derivatives, phenanthroline derivatives or perylene tetracarboxylic acid derivatives such as disclosed in Appl. Phys. Lett. 48 (2) (1986)183.
An electron transporting layer can be formed by preparing an organic film containing at least one electron transporting material on the hole transporting layer or on the light-emitting layer. The electron transporting layer can be formed by the vacuum deposition method, the spin-coating method, the casting method, the LB method and the like.
As in the case of forming a light emitting layer or a positive hole transporting layer by using a solution containing a polymer binder, a smoother and more homogeneous electron transporting layer can be formed by using a solution containing a binder and at least one electron transporting material.
The thickness of an electron transporting layer is preferably chosen in the range of from 0.5 nm to 1000 nm, preferably from 1 nm to 100 nm, more preferably from 2 to 50 nm.
Another embodiment relates to the use of the inventive compounds I and known compounds Ia as UV fluorescent materials for void detection. Especially preferred is the use for so-called OEM (original equipment manufacturer) applications such as automotive electrocoats and subsequent layers, for example primer surfacers, as well as industrial applications in general.
The present invention therefore relates to coating compositions comprising (a) an organic film-forming binder and (b) at least one compound of the formula I or Ia.
The coating composition is optionally solvent based, water based or solvent free.
Examples of coating materials are lacquers, paints, varnishes, powder coatings or electrocoats. These usually contain an organic film-forming binder in addition to other, optional components.
Preferred organic film-forming binders are epoxy resins, polyurethane resins, amino resins, acrylic resins, acrylic copolymer resins, polyvinyl resins, phenolic resins, urea resins, melamine resins, styrene/butadiene copolymer resins, vinyl/acrylic copolymer resins, polyester resins or alkyd resins, or a mixture of two or more of these resins, or an aqueous basic or acidic dispersion of these resins or mixtures of these resins, or an aqueous emulsion of these resins or mixtures of these resins, or hybrid systems based on, for example, epoxy acrylates.
More specifically, the alkyd resins can be water-dilutable alkyd resin systems which can be employed in air-drying form or in the form of stoving systems, optionally in combination with water-dilutable melamine resins; the systems may also be oxidatively drying, air-drying or stoving systems which are optionally employed in combination with aqueous dispersions based on acrylic resins or copolymers thereof, with vinyl acetates, etc.
The acrylic resins can be pure acrylic resins, epoxy acrylate hybrid systems, acrylic acid or acrylic ester copolymers, combinations with vinyl resins, or copolymers with vinyl monomers such as vinyl acetate, styrene or butadiene. These systems can be air-drying systems or stoving systems.
In combination with appropriate polyamine crosslinkers, water-dilutable epoxy resins exhibit excellent mechanical and chemical resistance. If liquid epoxy resins are used, the addition of organic solvents to aqueous systems can be omitted. The use of solid resins or solid-resin dispersions usually necessitates the addition of small amounts of solvent in order to improve film formation.
Preferred epoxy resins are those based on aromatic polyols, especially those based on bisphenols. The epoxy resins are employed in combination with crosslinkers. The latter may in particular be amino- or hydroxy-functional compounds, an acid, an acid anhydride or a Lewis acid or a blocked isocyanate. Examples thereof are polyamines, polyaminoamides, polysulfide-based polymers, polyphenols, boron fluorides and their complex compounds, polycarboxylic acids, 1,2-dicarboxylic anhydrides, pyromellitic dianhydride, of toluoyl di-iso-cyanates.
Polyurethane resins are derived from polyethers, polyesters and polybutadienes with terminal hydroxyl groups, on the one hand, and from aliphatic or aromatic polyisocyanates on the other hand.
Examples of suitable polyvinyl resins are polyvinylbutyral, polyvinyl acetate or copolymers thereof.
Suitable phenolic resins are synthetic resins in the course of whose construction phenols are the principal component, i.e. in particular phenol-, cresol-, xylenol- and resorcinol-formaldehyde resins, alkylphenolic resins, and condensation products of phenols with acetaldehyde, furfurol, acrolein or other aldehydes. Modified phenolic resins are also of interest.
The coating compositions may additionally comprise one or more components taken, for example, from the group consisting of pigments, dyes, fillers, flow control agents, dispersants, thixotropic agents, adhesion promoters, antioxidants, light stabilizers and curing catalysts.
The pigments are, for example, titanium dioxide, iron oxide, aluminium bronze or phthalocyanine blue.
Examples of fillers are talc, alumina, aluminium silicate, barytes, mica, and silica.
Flow control agents and thixotropic agents are based, for example, on modified bentonites.
Adhesion promoters are based, for example, on modified silanes.
The claimed fluorescent compounds can be added to the coating material during its preparation, for example during pigment dispersion by grinding, or they are dissolved in a solvent and the solution is then stirred into the coating composition.
In the preparation of the organic film-forming binder by addition polymerization or condensation polymerization of monomers, the claimed fluorescent compounds can be mixed in in solid form, or dissolved, with the monomers even prior to the polymerization reaction.
The inventive maleimides I and other compounds of the formula Ia as well as compounds belonging to the group of dyestuffs exhibiting edge fluorescence are used in amounts of preferably 0.01% to 5% by weight, more preferably from 0.5 to 1.0% by weight, based on the total solids of the formulation containing no fluorescent agent.
The coating materials can be applied to the substrate by the customary techniques, for example by spraying, dipping, spreading or electrodeposition. In many cases, a plurality of coats are applied. The claimed maleimides I or the known compounds Ia as well as compounds belonging to the group of dyestuffs exhibiting edge fluorescence usually are added primarily to the base layer (primer), however, they can also be added to the intermediate coat, for example a primer surfacer, or topcoat, as well. Depending on whether the binder is a physically, chemically or oxidatively drying resin or a heat-curing or radiation-curing resin, the coating is cured at room temperature or by heating (stoving) or by irradiation.
Once the coating compositions are cured, the corresponding coatings can be inspected with the use of a UV-lamp. Defects or voids as a result of misapplication or artificially applied defects can be easily detected, because the used fluorescent compounds exhibit intense fluorescence only at the voids (so-called xe2x80x9cedge fluorescencexe2x80x9d).
Hence, another preferred embodiment of this invention relates to a composition comprising a dyestuff exhibiting edge fluorescence.
A further preferred embodiment of this invention relates to a method of inspecting the surface of a body comprising the steps of:
(a) covering a surface with a composition comprising a compound exhibiting edge fluorescence,
(b) inspecting the thus covered surface with ultraviolet light for visible light, such being indicative of faults in the surface.
Preferably, inspection is done using a high intensity black light (UV-A, 320-400 nm), preferably under low light conditions. A suitable lamp is available from Spectronics Corporation Inc. (Westbury, N.Y.).
Preferably, the edge fluorescence exhibiting compound is a maleimide of formulae I or Ia are used, most preferably 1,1xe2x80x2-(1,2-ethanediyl)bis[3,4-diphenyl]-1H-pyrrole-2,5-dione 
A further preferred embodiment relates to an article of manufacture comprising:
a body having a surface to be covered; a layer of coating material on the surface of the body, fluorescing means blended with said coating material for emitting identifiable visible light in response to exposure to ultraviolet light.
Preferably, the fluorescing means is a compound of formula I or Ia, particularly preferred is 1,1xe2x80x2-(1,2-ethanediyl)bis[3,4-diphenyl]-1H-pyrrole-2,5-dione.
The claimed fluorescent compounds as well as the compositions allow easy quality assurance, instant possibility of repair, easy longer-term inspection. Further, compared to optical brighteners, a superior solubility is observed which makes an incorporation more easy. In addition, the claimed materials show fluorescence in the solid state, whereas optical brighteners must be soluble in the resin or polymer to exhibit fluorescence. The claimed compounds and compositions also show a superior photostability and none to less yellowing compared to optical brighteners upon UV-exposure, i.e. optical brighteners photochemically decompose under UV-light within less than 24 to 100 hours with formation of colored products leading to discoloration of e.g. white coatings. Also the claimed compounds and compositions migrate less than and contaminate the working environment less than optical brighteners. A big advantage is the exhibition of the so-called edge fluorescence meaning that fluorescence is observed only at voids and not at the whole surface which gives much better contrast compared to e.g. optical brighteners and allows also the detection of minor defects or damages. Too, the inventive compounds and composition have no or only minimal impact on the paint color in comparison to dyes, i.e. they can be even used in white pigmented systems. Further, the inventive materials are useful in dark and white pigmented systems where optical brighteners fail, i.e. in dark pigmented systems fluorescence and subsequently voids are difficult to detect in known systems, in white pigmented systems fluorescence is too intense (whole surface) which in turn makes it very difficult to identify voids in systems of the prior art. Finally, the found superior photostability of the inventive materials compared to optical brighteners allows long-term void detection, i.e. inspection after months or years after the application. Particularly, 1,1xe2x80x2-(1,2-ethanediyl)bis[3,4-diphenyl]-1H-pyrrole-2,5-dione is suitable for detecting defects such as craters (voids) and poor coverage: an unique edge fluorescence phenomenon is shown when a cured coating is scratched. The technique also works over uneven surfaces, e.g. weld seams.